Systems, apparatuses, and methods for removing fixed offshore platforms

ABSTRACT

Systems, apparatuses, and methods for removing fixed offshore platforms using a semi-submersible marine vessel are described. The semi-submersible marine vessel may comprise a main body, a mooring system, a lifting system, and a gate disposed at the second end. The main body may have an extended shape sized to house a fixed offshore platform oriented in a prone position. The main body may have a first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position. The lifting system may have a plurality of strand jacks and plurality of strand jack cables.

FIELD

The disclosure relates to systems, apparatuses, and methods for removing fixed offshore platforms in order to decommission steel piled jackets.

BACKGROUND

Current methods for decommissioning steel piled jackets are expensive and hazardous. In addition, there is no lifting device in the North Sea with capacity to remove an oil and gas field platform with a single lift off the seabed floor. (Refer to report by Oil and Gas UK October 2012). Obtaining lifting devices and/or machinery to remove steel piled jackets may be both economically and physically hazardous.

Exploitation of offshore oil and gas fields has created several thousand platforms, commonly referred to as “jackets”. In some implementations, the jackets may have a portion above water commonly referred to as “top-side” or “topsides.” Jackets may be constructed to depths of approximately 600 feet. Jackets may have formerly supported drilling, production, processing facilities and/or be fitted with risers extending from the seabed to the main deck. Some of the jackets may be several years old and may have severe corrosion problems necessitating the addition of clamps and/or cement boxes to hold them together. Corrosion of the jackets may make their removal in a single lift problematic, as the corroded members may fail abruptly when lifted or rotated. Rotating a corroded jacket 90° to pull the jacket onto a lifting vessel (e.g. a boat or barge) may be problematic and/or expensive.

Jacket rotation may be an expensive but necessary part of decommissioning a jacket and removal. Rotation may apply structural forces to the jacket structural members in directions and/or loads that the jacket may not have been designed to support. For example, one column of the jacket may Weigh 3000 tonnes and support axial compression and/or tension loads but fail in bending. The jacket may weigh 30,000 tonnes creating large bending moments in a rotating jacket. As such, catastrophic structural collapse may result during rotation of the jacket.

SUMMARY

One aspect of the disclosure relates to a semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets. The semi-submersible marine vessel may comprise a main body, a mooring system, a lifting system, and a gate disposed at the second end. The main body may have an extended shape sized to house a fixed offshore platform oriented in a prone position. The main body may have a first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position. The lifting system may have a plurality of strand jacks and plurality of strand jack cables.

Another aspect of the disclosure relates to a method for decommissioning fixed offshore platforms such as steel piled jackets. The method may include maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket. The semi-submersible marine vessel may comprise a main body, a mooring system, a lifting system, and a gate disposed at the second end. The main body may have an extended shape sized to house a fixed offshore platform oriented in a prone position. The main body may have a first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position. The lifting system may have a plurality of strand jacks and plurality of strand jack cables. The method may include opening the gate. The method may include surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body. The method may include attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket. The method may include affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting or rotating the fixed offshore platform jacket. The method may include deballasting the main body in order to free the offshore platform jacket from seabed. The method may include rotating the fixed offshore platform jacket under water from a vertical position to a prone position. The method may include housing the fixed offshore platform jacket oriented in the prone position within the main body to enable transport of the semi-submersible marine vessel towards a dry-dock. The method may include closing the gate. The method may include guiding the semi-submersible marine vessel towards the dry-dock.

Another aspect of the disclosure relates to a semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets. The semi-submersible marine vessel may comprise a main body, a mooring system, and a lifting system having a plurality of strand jacks and a plurality of strand jack cables. The main body may be sized to surround a portion of a fixed offshore platform oriented in a vertical position. The main body may have a first end and a first side opposing a second side, the first end having dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position, the first side and the second side having dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension.

Another Aspect of the disclosure relates to a method for decommissioning fixed offshore platforms such as steel piled jackets. The method may include maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket. The semi-submersible marine vessel may comprise a main body, a mooring system, and a lifting system having a plurality of strand jacks and a plurality of strand jack cables. The main body may be sized to surround a portion of a fixed offshore platform oriented in a vertical position. The main body may have a first end and a first side opposing a second side, the first end having dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position, the first side and the second side having dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension. The method may include opening the gate. The method may include surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body. The method may include ballasting the main body so that a lower portion of the main body is submerged in the water. The method may include attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket. The method may include affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting. The method may include deballasting the main body in order to free the offshore platform jacket from a seabed. The method may include housing the fixed offshore platform jacket oriented in the vertical position within the main body to enable transport of the fixed offshore platform jacket above the seabed surface. The method may include closing the gate. The method may include guiding the semi-submersible marine vessel towards a higher elevation along an inclined surface of seabed. The method may include setting the fixed offshore platform jacket down vertically on the inclined surface of seabed. The method may include cutting an exposed top portion of the fixed offshore platform jacket. The method may include loading the cut potion on a barge in order to be shipped to shore for further processing. The method may include repeating the previous steps as necessary to completely remove the fixed offshore platform jacket from water.

These and other features, and characteristics of the present technology, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents, unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a semi-submersible platform, in accordance with one or more implementations.

FIG. 2 illustrates a system for transporting material from the seabed to a semi-submersible platform on the surface of the sea, in accordance with one or more implementations.

FIG. 3 illustrates a semi-submersible vessel configured to store liquids, in accordance with one or more implementations.

FIG. 4 illustrates a portion of a semi-submersible vessel configured to store liquids, in accordance with one or more implementations.

FIG. 5 illustrates a cross-sectional view of a semi-submersible vessel configured to store material, in accordance with one or more implementations.

FIG. 6 illustrates a floating dock moored around a jacket and ready to lift and rotate the jacket to the horizontal, in accordance with one or more implementations.

FIG. 7 illustrates a semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets, in accordance with one or more implementations.

FIGS. 8(A) and 8(B) illustrate the lower portion of a semi-submersible marine vessel configured for removing fixed offshore platforms, in accordance with one or more implementations.

FIGS. 9(A)-9(D) illustrate a method for decommissioning fixed offshore platforms such as steel piled jackets at various stages, in accordance with one or more implementations.

FIG. 10 illustrates a method for decommissioning fixed offshore platforms Such as steel piled jackets, in accordance with one or more implementations.

FIG. 11 illustrates another semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets, in accordance with one or more implementations.

FIGS. 12(A) and 12(B) illustrate the lower portion of another semi-submersible marine vessel configured for removing fixed offshore platforms, in accordance with one or more implementations.

FIG. 13 illustrates another method for decommissioning fixed offshore platforms such as steel piled jackets at various stages, in accordance with one or more implementations.

FIG. 14 illustrates another method for decommissioning fixed offshore platforms such as steel piled jackets, in accordance with one or more implementations.

DETAILED DESCRIPTION

Deepwater moorings present difficulties in the use of chain or cable for a number of reasons. For example, the angle of catenary in the portion of the chain or cable adjacent to the semi-submersible platform is typically too steep to provide significant lateral restraint until the vessel is significantly off-station. The density of the chain may be so great that its own weight may cause fatigue in the chain, leaving no margin of error for environmental forces. Such situations cause the chains to fatigue prematurely, necessitating continual monitoring and maintenance, as well as inspection by regulatory authorities.

FIG. 1 illustrates a floating production system 100, in accordance with one or more implementations. The floating production system 100 may be configured to float on the sea surface 102. The floating production system 100 may comprise a superstructure 104 configured to float on the sea surface 102. The superstructure 104 may have a first portion 106 that is configured to rest above the surface of the sea 102 and a second portion 108 that is configured to rest below the surface of the sea 102. The floating production system 100 may comprise a mooring system 110 configured to moor the superstructure 104 to the seabed 112.

Removing steel jackets can be a dangerous and expensive process. In some implementations, removal of the exposed topsides by cutting and hauling the exposed sections of the jacket may be accomplished before the jacket is removed in its entirety. For example if the top-side has been removed and only jacket structure remains a MPSS, ESSS, and/or other floating dock may be moored around the jacket. In some implementations, this may be accomplished using conventional moorings for the prevailing water depth. The jacket may be lifted and/or rotated to sit within the floating dock's confines and/or above the floating docks bottom. The dock gates may be dosed at both ends to surround the jacket.

The mooring system 110 may comprise a first end 114. The first end 114 may be operatively connected to the superstructure 104. The first end 114 may be configured to secure the mooring system 110 to the superstructure 104. The mooring system 110 may comprise a second end 116. The second end 116 may be configured to secure the mooring system 110 to the seabed 112. The mooring system 110 may comprise a neutrally buoyant line 118. The neutrally buoyant line 118 may be disposed between the first end 114 and the second end 116 of the mooring system 110. The neutrally buoyant line 118 may be configured to facilitate the mooring of the superstructure 104 to the seabed 112.

The mooring system 110 may comprise neutrally buoyant line(s) 118 suspended from the semi-submersible platform 100. The neutrally buoyant line(s) 118 may be suspended in a relatively straight line. The neutrally buoyant line(s) 118 may connect with an upper chain and a lower chain. The neutrally buoyant line(s) 118 may be configured to have relatively equal tension at the top, as the tension at the bottom of the neutrally buoyant line(s) 118. The mooring system 110 may comprise multiple neutrally buoyant lines 118 suspended in catenary to form a curtain of neutrally buoyant lines 118. The curtain of neutrally buoyant mooring lines 118 suspended in catenary may provide horizontal force. The horizontal force provided by the neutrally buoyant mooring lines 118 suspended in catenary may facilitate maintaining the semi-submersible platform 118 over a desired area of the seabed. The multiple neutrally buoyant mooring lines 118, suspended in a catenary curtain, may comprise a section of the mooring system 110. The mooring system 110 may comprise multiple sections. For example, the mooring system may comprise a mooring section, a first side of the semi-submersible platform 100, and a mooring section on a second side of the semi-submersible platform 100. Mooring sections may be disposed on multiple sides of the semi-submersible platform 100. In some implementations, mooring sections may be disposed at and/or near the corners of the semi-submersible platform 100.

The neutrally buoyant line 118 may comprise a first line portion 120. The first line portion 120 may extend from the superstructure 104 through a first upper portion 120 of the neutrally buoyant line 118. The second line portion 122 may extend from the seabed 112 through a second lower portion 122 of the neutrally buoyant line 118. The first line portion 120 and/or the second line portion 122 may comprise a chain, a cable, and/or a combination thereof. The neutrally buoyant line 118 may comprise a neutrally buoyant pipe portion 124. The neutrally buoyant pipe portion 124 may extend between the first upper portion 120 and the second lower portion 122 of the neutrally buoyant line 118. The neutrally buoyant pipe portion 124 may have a length of the depth of the sea, i.e., the distance between the sea surface 102 and seabed 112. The neutrally buoyant pipe portion 124 may have a length of up to four times the depth of the sea, i.e., four times the distance between the sea surface 102 and seabed 112. The neutrally buoyant pipe portion 124 may have a length selected to comply with one or more parameters. The length of the neutrally buoyant pipe portion 124 may be selected to provide a pre-selected tension or range of tension in the neutrally buoyant pipe portion 124.

The neutrally buoyant pipe 124 may comprise pipe having a variety of diameters. The neutrally buoyant pipe 124 may comprise pipe having a variety of wall thicknesses. The neutrally buoyant line 118 may comprise a negatively-buoyant portion. The negatively-buoyant portion may be disposed toward the lower portion of the neutrally buoyant line 118. The neutrally buoyant line 118 may comprise a positively-buoyant portion. The positively-buoyant portion may be disposed toward the upper portion of the neutrally buoyant line 118. By using such a mooring system 110, the horizontal mooring stiffness may be increased. Increasing the horizontal mooring stiffness may decrease the offset of the semi-submersible platform 100, compared to using solid chains and/or cables. By using such mooring systems 110, the weight of the mooring system is less than using solid chains and/or cable, making the mooring system safer and easier to use.

The neutrally buoyant pipe 124 may comprise seals 132. The seals 132 may be disposed at either end of the neutrally buoyant pipe 124. The neutrally buoyant pipe 124 may comprise multiple seals 132 disposed along the neutrally buoyant pipe 124. The neutrally buoyant pipe 124 may comprise multiple sections of neutrally buoyant pipe. Each section of neutrally buoyant pipe may comprise seals.

The second end 116 of the mooring system 110 may comprise an anchor 126. The anchor 126 may be configured to anchor the mooring system 110 to the seabed 112. The second end 116 of the mooring system 110 may comprise a deadweight 128. The deadweight 128 may be configured to counteract the buoyancy of the neutrally buoyant pipe 124. The neutrally buoyant line 118 may comprise floats 130 disposed at intervals along the neutrally buoyant line 118 to provide buoyancy to the neutrally buoyant line 118.

In some implementations, the buoyancy of the buoyant line 118 may facilitate the moorings to be pre-laid. The neutrally buoyant lines 118 may be fitted with pennant buoys. The pennant buoys may be configured such that they may be retrieved from the sea. The pennant buoys may be configured such that they may be connected to the semi-submersible platform 100. The connection may be facilitated by anchor-handling tugs.

In some implementations, the upper portion 120 of the neutrally buoyant line 118 may pass through a lower bearing 134. The lower bearing 134 may be attached to the second portion 108 of the semi-submersible platform 100. The lower bearing 134 may be a swivel fairleader. In some implementations, the upper portion 120 of the neutrally buoyant line 118 may be connected to the superstructure 104 of the semi-submersible platform 100. The upper portion 120 of the neutrally buoyant line 118 may be connected to the superstructure 104 of the semi-submersible platform 100 by a second bearing 136. The second bearing 136 may be configured to facilitate the tensioning of the neutrally buoyant line 118 to a desired level of tension.

The mooring system 110 may be arranged in catenary. The lines comprising the neutrally buoyant lines 118 may be disposed in catenary to avoid bending moments in the lines. The lines arranged in catenary may provide increased horizontal tension on the floating production system to facilitate the floating production system to remain in location. The angle of the buoyant mooring line 118 at the top of the mooring system 110 may be provided by the following equations:

${xp}_{k}:={A\; 1\; a\; {{\cos h}\left( \frac{D_{0,k} + {A\; 1}}{A\; 1} \right)}}$ ${\Psi 1}_{k}:={a\; {\tan \left( {{\sin h}\left( \frac{{xp}_{k}}{A\; 1} \right)} \right)}}$ ${T\; 1_{k}}:={{\frac{HT}{\cos \; {\Psi 1}_{k}}{T2}_{k}}:=\left\lbrack {\left( {T\; 1_{k}} \right)^{2} + G^{2} + {2T\; 1_{k}G\; {\sin \left( {\Psi 1}_{k} \right)}}} \right\rbrack^{\frac{1}{2}}}$ ${\Delta\Psi}_{k}:={a\; {\cos \left\lbrack \frac{\left\lbrack {\left( {T\; 1_{k}} \right)^{2} + \left( {T\; 2_{k}} \right)^{2}} \right\rbrack - G^{2}}{2T\; 1_{k}T\; 2_{k}} \right\rbrack}}$

The double catenary profile may be provided by the following equations:

x0_(k) := xp_(k) ⋅ (−1) + A 2 ⋅ a sin h(tan (Ψ1_(k) + Ψ_(k))) ${y0}_{k}:={{A\; {2 \cdot \left( {{\cosh \left( \frac{{xp}_{k} + {x\; 0_{k}}}{A\; 2} \right)} - 1} \right)}} - {A\; {1 \cdot \left( {{\cosh \left( \frac{{xp}_{k}}{A\; 1} \right)} - 1} \right)}}}$ ${xs}_{k}:={{A\; {2 \cdot a}\; {\cosh \left( \frac{S + {y\; 0_{k}} + {A\; 2}}{A\; 2} \right)}} - {x\; 0_{k}}}$

The catenary length may be provided by the following equations:

${l\; 1_{k}}:={A\; {1 \cdot {\sinh \left( \frac{{xp}_{k}}{A\; 1} \right)}}}$ ${l\; 2_{k}}:={A\; {2 \cdot \left( {{\sinh \left( \frac{{xs}_{k} + {x\; 0_{k}}}{A\; 2} \right)} - {\sinh \left( \frac{{xp}_{k} + {x\; 0_{k}}}{A\; 2} \right)}} \right)}}$ x_(k) := xs_(k) − l 1_(k) i := 0  …  100 ${z\; 1_{i,k}}:={{{- l}\; 1_{k}} + {\frac{{xp}_{k}}{100} \cdot i}}$ ${z\; 2_{i,k}}:={{{- l}\; 1_{k}} + {xp}_{k} + {\left( \frac{{xs}_{k} - {xp}_{k}}{100} \right) \cdot i}}$ ${y\; 1_{i,k}}:={A\; {1 \cdot \left( {{\cosh \left( \frac{{z\; 1_{i,k}} + {l\; 1_{k}}}{A\; 1} \right)} - 1} \right)}}$ ${y\; 2_{i,k}}:={{{- y}\; 0_{k}} + {A\; {2 \cdot \left( {{\cosh \left( \frac{{z\; 2_{i,k}} + {l\; 1_{k}} + {x\; 0_{k}}}{A\; 2} \right)} - 1} \right)}}}$

The length of the line may be any length. For example, the length of the line may be in excess of 3×10⁴ meters (e.g. l2₁=3.123×10⁴). The length of the line may be dependent on a number of factors. One such factor may be the depth of the ocean at the location of the floating production system. Another factor may be ocean currents, the density of the line, and/or other factors. The tension at the end of the line may be provided by:

VT_(k) := l1_(k) ⋅ μ1 + l 2_(k) + μ2 + G $T_{K}:=\sqrt{{HT}^{2} + \left( {VT}_{k} \right)^{2}}$ $\Phi_{k}:={{{a\tan}\left( \frac{HT}{{VT}_{k}} \right)} \cdot \frac{180}{\pi}}$

Most risers presently used are hoses. Such hoses may be expensive and represent a large percentage of the field investment. Hoses may be pressure limited and necessitate the use of complex seabed equipment, including chokes, to reduce oil pressure on the seabed prior to entry to the hose. Hoses and the seabed equipment are typically cumbersome and expensive to manufacture and implement. In some instances, wells may be combined through manifolds to reduce the total number of hoses. Preventing cross-circulation between wells requires implementation of multiple check valves, which are prone to failure. (40) FIG. 2 illustrates a system 200 for transporting material from the seabed 202 to a semi-submersible platform 204 on the surface 206 of the sea, in accordance with one or more implementations. The system 200 for transporting material from the seabed 202 to a semi-submersible platform 204 on the surface 206 of the sea may comprise two or more pipes 208 disposed between the seabed 202 and a semi-submersible platform 204. The semi-submersible platform 204 may be configured to float on the surface 206 of the sea. The pipes 208 may have a first end 210 extending toward the semi-submersible platform 204. The pipes 208 may have a second end 212 extending toward the seabed 202. The pipes 208 may be configured to facilitate the transport of liquid material from the seabed 202 toward the surface 206 of the sea.

The system 200 for transporting material from the seabed 202 to the semi-submersible platform 204 may comprise a pipe anchor 214. The pipe anchor 214 may be configured to anchor at least one pipe 208 to the seabed 202. The system 200 for transporting material from the seabed 202 to the semi-submersible platform 204 may comprise a pipe connector 216 configured to secure at least one pipe 208 to the semi-submersible platform 204. The pipe connector 216 may be configured to facilitate the transfer of liquid material between the pipes 208 and the semi-submersible platform 204.

The two or more pipes 208 may be arranged in catenary. The two or more pipes 208 may be arranged in a coplanar curtain. The radii 218 of the bends 220 in the pipes 208 may be configured to be above a fatigue threshold.

The system 200 for transporting material from the seabed 202 to the semi-submersible platform 204 may comprise a bearing 222. The bearing 222 may be disposed on the semi-submersible platform 204. The bearing 222 may be configured to secure the two or more pipes 204 to the semi-submersible platform 204. The bearing 222 may be configured to reduce the bend moments in the two or more pipes 208. The bearing may be adapted to facilitate the control of the bend 220 of the radii 218 of the two or more pipes 208 arranged in catenary.

The system 200 for transporting material from the seabed 202 to the semi-submersible platform 204 may comprise a ground riser 224. The ground riser 224 may be configured to secure the two or more pipes 208 to the seabed 202. The system 200 for transporting material from the seabed 202 to the semi-submersible platform 204 may comprise an anchor template. The anchor template may be configured to secure the two or more pipes 208 to the seabed 202. The anchor template may be configured to withstand horizontal forces applied on the anchor template by the two or more pipes 208 in catenary. The anchor template may be configured to facilitate decoupling of the two or more pipes 208.

Well pressure may be applied to the pipes 208 in catenary without exceeding a threshold stress level in the pipes 208. Such systems 200 may comprise chokes 226. The chokes 226 may be operatively connected to the pipes 208. The chokes 226 may be placed on the deck 228 of the semi-submersible platform 204.

The catenary pipes 208 may be formed of any suitable material. The suitable material may have relatively high strength. The suitable material may have corrosion resistant properties. For example, the catenary pipes 208 may be formed from one or more of steel, aluminum, titanium, metal alloys, composites, plastics, and/or other suitable material. The catenary pipes 208 may be configured to facilitate the transport of water, gas, and/or other fluids. The system 200 may be configured to facilitate the transport of fluids from the sea surface 206 to the seabed 202. For example, the system 200 may be configured to facilitate water injection, gas reinjection, and/or other fluid transport. Internally clad pipes may be used for the transport of corrosive fluids.

The system 200 may comprise a second pipe encasing the catenary pipes 208. The second pipes may be configured to provide an additional barrier to guard against unintentional leaks and/or damage to the pipes 208.

Crude oil may be stored in a semi-submersible vessel using a seawater displacement system. The semi-submersible vessel may be a platform, a submerged barge, a grounded barge, and/or other vessel capable of storing liquid material. The semi-submersible vessel may comprise a steel ring pontoon, columns, or legs, and a deck. The steel ring pontoon, columns, and deck may be structurally integrated. The steel ring pontoon, columns, and deck may be structurally independent. Crude oil may be stored within storage tanks disposed in the pontoons and/or columns of the semi-submersible vessel. The storage tanks may be filled with water to provide ballast. The ballast water may cause the semi-submersible vessel to have a desired amount of draft. The ballast water may be ejected from the tanks in response to receiving an amount of crude oil into the tanks. The semi-submersible vessel may comprise secondary tanks to facilitate the adjustment of draft, stability, and/or other parameters of the semi-submersible vessel.

Typical systems for storing crude oil at off-shore production facilities include storage tanks distributed along long ship-shaped vessels. The storage tanks were typically only partially filled. Partially-filled storage tanks leave ullage, a space between the surface of the oil and the top of the storage tank. The atmosphere of the ullage is typically corrosive, humid, and can cause corrosion of the tanks. Acids may form, which may corrode the tanks, steel deck supports, deck plating, and other structural elements of the storage vessels. Protective coatings are costly and have limited effectiveness and shelf-lives.

FIGS. 3 and 4 illustrate a semi-submersible vessel 300 configured to store liquids, in accordance with one or more implementations. The semi-submersible vessel 300 may comprise an upper portion 302 configured to provide a platform 304. The semi-submersible vessel 300 may comprise a lower portion 306. The lower portion 306 of the semi-submersible vessel 300 may comprise vertically-disposed legs 308 extending downward from the upper portion 302. The lower portion 306 of the semi-submersible vessel 300 may comprise a horizontally-disposed pontoon 310. The pontoon 310 may extend between at least two of the legs 308. The pontoon 310 may extend between at least two of the legs 308 adjacent to the end of the legs opposite to the upper portion 302.

The semi-submersible vessel may be configured to have a regular four-sided shape. The dimensions of the semi-submersible vessel may be selected based on one or more environmental parameters. For example, the width, length and/or height of the semi-submersible vessel may be selected, based on the water depth of the intended operational location for the semi-submersible platform, a characteristic of the environment conditions of the intended operational location for the semi-submersible platform. The intended operational location may include the location in which the semi-submersible platform will be based, used, or the location that it may be transported through.

Test results have shown that the semi-submersible vessel can be scaled to any dimension and provide for satisfactory hydro-dynamic and static variables. Various ratios may be employed between the various dimensions of the semi-submersible vessel. For example only, a column breadth may equal a size C. The column width may be selected to equal or substantially equal the column breadth, i.e. size C. The column height may be selected to equal a multiple of the column breadth and/or width. One such selected height may be equal to six times C. The distance between adjacent columns may be selected to be a multiple of the column breadth and/or width. For example, the selected distance between adjacent columns may be selected to be four time C. The height of the pontoons may be selected to be a multiple of the column breadth and/or width. For example, the pontoon height may be selected to be a half of C. The depth of the main deck may be selected to be a multiple of the column breadth and/or width. For example, the depth of the main deck may be selected to be a quarter of C.

The dimensions, ratios, and/or scales provided herein are to provide examples only and are not intended to be limiting. The disclosed inventive concepts are intended to cover semi-submersibles and/or floating production platforms having any ratio, size, dimensions and/or other parameters.

A software system may be provided to aid in the development and design of the floating production platform. The software system may be implemented using one or more physical computer processors. The one or more physical computer processors may be configured to execute machine-readable instructions to facilitate the development and design of the floating production platform.

The software system may be configured to receive, from a user, a selection and/or entry of one or more parameters defining a size of the vessel. The one or more size parameters may include a width, breadth, height, and/or other size parameter. The software system may be configured to receive, from a user, a selection and/or entry of one or more element parameters. The system may comprise a database of elements that are selectable by the user. In some implementations, the system may be configured to allow selection and/or entry of dimensions of elements by a user. The elements may represent construction elements, such as welded blocks that will make up the structure of the floating production system. The elements may be arranged in layers, such that the bottom layers may be the first layer. Additional elements placed on top of the bottom layers may be designated the second layer, third layer, and so on.

The software system may be configured to facilitate the selection and/or entry of the individual layers. The software system may be configured to facilitate manipulation by the user of the individual layers in response to selection and/or entry of the individual layers.

The software system may be configured to facilitate the selection and/or entry of individual and/or groups of elements to be ballasted. The software system may be configured to facilitate the selection and/or entry of a type of ballast. For example, a ballast type may be water, oil, and/or a combination thereof.

The software system may be configured to facilitate selection and/or entry of a draught for the vessel. In response to selection and/or entry of a draught for the vessel by a user, the software system may be configured to provide an indication of the amount of ballast needed to achieve the selected and/or entered draught. The software system may be configured to provide an indication of recommended locations for the ballast based on one or more parameters of the floating production system being designed. Such parameters may include maintaining a desired centered of gravity, or range for the center of gravity, during certain operating conditions.

The software system may be configured to facilitate selection of a viewing angle by a user, such that the user may change the viewing angle to a desired viewing angle.

The software system may be configured to facilitate the selection and/or entry of loads to be added to the vessel. Facilitating selection and/or entry of loads to be added to the vessel may include selection and/or entry of a location to place the loads. Facilitating selection and/or entry of loads to be added to the vessel may include selection and/or entry of a type of load, such as fixed load or moving load.

The software system may be configured to perform calculations based on the parameters of the designed vessel. The software system may be configured to determine whether the designed vessel meets predefined fit-for-purpose parameters. The software system may be configured to provide an indication of dimensions and/or elements of the designed vessel that need to be changed to comply with the fit-for-purpose parameters. The software system may be configured to provide suggested changes to be made to the designed vessel so that the vessel will comply with the fit-for-purpose parameters.

The semi-submersible vessel may have a size selected based on a number of parameters. The parameters may include payload parameters, environmental parameters, aesthetic parameters, functionality parameters, and/or other parameters. The dimensions of the semi-submersible vessel may be any size. For example, the length and/or width of the main deck of the semisubmersible vessel may be less than 30 meters or may extend beyond 120 meters. The depth of the main deck may be determined based on desired payload and/or weight distribution of desired equipment.

The lower portion 306 may be configured to provide sufficient buoyancy to maintain the upper portion 302 substantially above the water 312. The lower portion 306 may be configured to store liquid matter 314. The liquid matter 314 stored in the lower portion 306 may comprise one or more of sea water, ballast water, and/or crude oil. The lower portion 306 may be configured to store two or more types of liquid matter. For example, the lower portion 306 may be configured to store an amount of a first type of liquid matter. The lower portion 306 may be configured to fill the remaining volume of the lower portion 306 with a second type of liquid matter. The lower portion 306 may comprise one or more storage tanks. The one or more storage tanks may be comprised to store liquid material. The one or more storage tanks may be comprised to store multiple types of liquid material. The one or more storage tanks may be comprised to store a first amount of a first type of liquid material. The one or more storage tanks may be configured to fill the remaining volume of the storage tanks with a second type of liquid material.

The lower portion 306 may be comprised of tubular elements. The tubular elements may resemble rectangular blocks. The lower portion may comprise a plurality of cubic boxes 316. Individual rectangular tubular elements and/or cubic boxes 316 may be operably connected to adjacent rectangular tubular elements. The rectangular tubular elements and/or cubic boxes may be connected through one or more of welding, riveting, sticking, mechanical seal, construing, and/or other connecting methods. The rectangular tubular elements and/or cubic boxes may be formed of metal. The rectangular tubular elements and/or cubic boxes may be formed from an alloy. The rectangular tubular elements and/or cubic boxes may be formed of steel. As used herein, the term rectangular tubular elements is intended to encompass tubular elements having walls with equal dimensions, forming a square, as well as tubular elements having walls with different dimensions.

The end walls 318 of the blocks may form bulkheads between adjacent cubic boxes. The end walls 318 may form a second protective layer for storage tanks disposed within the cubic boxes.

The lower portion 306 of the semi-submersible vessel 300 may be configured to receive an amount of crude oil for storage. The lower portion 306 of the semi-submersible vessel 300 may be configured to eject an amount of ballast water. The lower portion 306 of the semi-submersible vessel 300 may be configured to eject an amount of ballast water in response to receiving an amount of crude oil for storage. The amount of ballast water ejected may be an amount corresponding to the amount of crude oil received for storage. The amount of ballast water ejected may be an amount selected based on a determination made to meet one or more parameters. The determination may be based, at least in part, on the amount of crude oil received, or to be received, for storage.

The semi-submersible vessel 300 may comprise filtration tanks 320. The filtration tanks 320 may be configured to receive and/or filter one or more contaminants from the ejected ballast water. The filtration tanks 320 may be configured to eject filtered ballast water into the sea.

FIG. 5 illustrates a semi-submersible platform 500 wherein the pontoons 502 are configured to store liquid. In particular, the pontoons 502 may be configured to store oil. The pontoons 502 may be configured to store ballast. In some implementations, the ballast may comprise sea water. The pontoon 502 may comprise a keel 504 and a deck 506. The deck 506 may be configured to be parallel with the keel 504. The deck 506 may be configured to have a slope relative to the keel 504. The slope of the deck 506 relative to the keel 506 may be less than one degree, approximate one degree, one degree, or more than one degree. The deck 506 may be configured to have a variable slope relative to the keel 504. (69) The semi-submersible platform 500 may be configured to trim to facilitate emptying of the tanks and/or cleaning.

The pontoon 502 may have a storage portion 508. The storage portion 508 of the pontoon 502 may comprise tanks. The storage portion 508 of the pontoon 502 may comprise linings. The linings may protect the structure of the pontoon 502 from harmful effects of the material stored within the pontoon 502. The storage portion 508 may be configured to store sea water, oil, other material and/or a combination thereof. The storage portion 508 of the pontoon 502 may have a designated minimum level 510 for one or more stored materials. For example, when the pontoon 502 is configured to store one or more of oil or water, there may be a minimum material level 510 of the water or oil in the storage portion 508 of the pontoon 502. In the example where oil and water are stored in the pontoon 502, the minimum level 510 may be the minimum level of water in the storage portion 508 of the pontoon 502. The storage portion 508 of the pontoon 502 may have a designated maximum material level 512 for the material stored on the storage portion 508 of the pontoon 502. The designated maximum material level 512 may be the maximum level of the combined materials in the storage portion 508 of the pontoon 502.

In one example, where the pontoon 502 is configured to store oil and water, the minimum material level 510 may be minimum water level in the pontoon 502. The oil, crude oil, dead crude oil and/or combination thereof, herein referred to as “oil”, may be stored in the pontoon with the water. The hydrophobic nature of oil may cause a water-oil interface to form wherein the oil is disposed in the pontoon 502 above the water.

Water, for example sea water, may be placed into the pontoon 502 to provide a stabilizing effect for the semi-submersible vessel 500. Water may be placed into the pontoon 502 to eliminate ullage. Water may be placed into the pontoon 502 to reduce the differential pressure on the pontoon 502. When oil is provided to the pontoon 502 for storage, the water, acting as ballast, may be extracted from the pontoon 502. VVhen oil is provided to the pontoon 502 for storage, the water may be displaced from the pontoon 502. The water and oil stored in the pontoon 502 may provide the necessary stability for the semi-submersible vessel 500. When oil is removed from the pontoon 502, water may be introduced to continue to provide stability to the semi-submersible vessel 500. When oil is removed from the pontoon 502, water may be introduced to control differential pressure.

When the pontoon 502 is submerged, the tanks in the pontoon 502 may be submerged. Submerging the pontoons 502 may reduce the pressure differential on the pontoons 502. Reducing the pressure differential on the pontoons 502 may facilitate the use of lighter materials to construct the pontoons 502.

When water is removed from the pontoon 502 it may pass through filtration systems 514. The water may be removed through a water removal pipe 516. The water removal pipe 516 may have an entry end 518. The entry end 518 of the water removal pipe 516 may be disposed in the pontoon 502 at a level below the minimum material level 510 for material stored in the pontoon 502. Water may be added to the pontoon 502 to provide ballast to the pontoon 502. Water may be obtained from the sea. Water from the sea may be obtained and passed through a filtration system 520 to filter the sea water before being provided to the pontoon 502. The water may be provided to the storage portion 508 of the pontoon 502 through a diffuser 522. The diffuser 522 may be disposed within the storage portion 508 of the pontoon 502 below the designated minimum material level 510.

Material may be provided to the pontoon 502 for storage. The material, such as oil, may be provided by a material storage pipe 524. The material storage pipe 524 may comprise an exit end 526. The exit end 526 may be disposed in and/or at the pontoon 502 to provide material to the pontoon 502 for storage. The exit end 526 of the material storage pipe 524 may be positioned at the top of the pontoon 502. The exit end 526 of the material storage pipe 524 may be fitted with a diffuser, baffle plate, and/or may be dynamically positioned such that the distance between the end of the storage pipe 524 and the top of the stored material and/or combined material, in the pontoon 502 is less than a threshold distance. The exit end 526 of the material storage pipe 524 may be positioned, stationary or dynamically varied, to be below the surface of the stored material in the pontoon 502.

The stored material, such as oil, in the pontoon 502, may be extracted from the pontoon 502. A material extraction pipe 528 may facilitate the extraction of the material from the pontoon 502. The material extraction pipe 528 may comprise an extraction end 530. The extraction end 530 may be disposed in the pontoon 502. The extraction end 502 may be disposed below the surface of the material to be extracted, such as oil. The extraction end 530 may be disposed above the minimum material level 510. Positioning the extraction end 530 above minimum material level 510 may avoid extracting water with the material. The extraction end 530 may be configured to be dynamically positioned. The extraction end 530 may be stationary. When the material, such as oil, is extracted through the extraction pipe 528, replacement material, such as sea water may be introduced into the pontoon 502. Introducing the water into the pontoon 502 may cause the material to be extracted, such as oil, to maintain an upper level position.

The semi-submersible platform 500 of the floating production system may comprise multiple oil storage tanks. The oil storage tanks may be disposed in the pontoons 502 of the semi-submersible platform 500. The pontoons may facilitate a single storage tank. The pontoons may facilitate multiple storage tanks. The storage tanks may be disposed in other elements of the semi-submersible platform 500. The storage tanks may be interconnected. The storage tanks may be interconnected using cross-levelling valves. In some implementations, the cross-levelling valves may be open during working conditions, when the floating production system is being used to extract materials. The ross-levelling valves may be closed during transit.

In some implementations, ballast water may be supplied to the tanks through free-flooding valves. In some implementations, ballast water may be supplied to the tanks, facilitated by the use of pumps.

In some implementations, the semi-submersible platform may comprise a deck structure. The deck structure may be configured to contain elements of the floating production system. For example, the floating production system may comprise living quarters, process and utilities elements, power generation elements, control modules, safety system elements, flare handling elements, mechanical handling system elements, and/or other elements.

The storage tanks may comprise anti-corrosive paint, sacrificial anodes, hot blast aluminum coatings, and/or other elements to reduce corrosion inside and/or outside of the tanks and/or pontoons.

In some implementations comprising multiple storage tanks, the storage tanks may be filled and/or emptied at approximately the same rate. Cross-levelling valves may facilitate the equalization of the pontoons and/or tanks.

In some implementations, the floating production platform may be installed at a location. The pontoons 502 and/or storage tanks may be flooded with ballast water to the waterline level. Oil and/or other material, may be provided to the storage tanks. The oil and/or other material provided to the storage tanks may displace the water.

A multi-stage settling tank system may be implemented to remove contaminants from the displaced water. A filtration and/or treatment system may be implemented to remove contaminants from the displaced water. The water filtration system may comprise multiple settling tanks, including a first tank and a second tank. Water may be removed from the bottom of the first tank and introduced to the top of the second tank. The water may be removed using a pump. The water filtration system may comprise a contaminant separator. The contaminant separator may be configured to remove contaminants from the water. The contaminant separator may be configured to scrub the water such that is complies with IMO and/or MARPOL requirements.

The pontoons 502 may comprise protection systems. The protection systems may comprise fendering systems to provide protection against damage caused by collisions with the pontoons 502.

The floating production system may comprise a trimming system. The trimming system may comprise one or more sets of trimming tanks. The sets of trimming tanks may be disposed in the leg portions, or columns, of the floating production system. Pneumatic and/or hydraulic pumping systems may facilitate the control of valves and/or pumps, which facilitate the introduction or removal of water from the sets of trimming tanks. The trimming system may perform functions automatically. The trimming system may be manually controlled. The trimming system may be configured to remove water and/or other ballast material from a first set of tanks in a first leg portion to a second set of tanks in a second leg portion of the floating production system. In some implementations the floating production system, it may be configured to operate having a slight trim. Providing a slight trim may facilitate the avoidance of air pockets forming in the one or more tanks.

A method of mooring a floating production system is disclosed. The method may comprise mooring the superstructure to the seabed. Mooring the structure to the seabed may comprise providing a mooring system having a first end operatively connected to the superstructure and configured to secure the mooring system to the superstructure. Mooring the structure to the seabed may comprise providing a mooring system with a second end that is configured to secure the mooring system to the seabed. Mooring the structure to the seabed may comprise providing at least one line between the first and second ends, wherein the line is arranged in catenary.

A method for transporting liquids between the seabed and a semi-submersible platform is provided. The method may comprise the steps of providing one or more pipes disposed between the seabed and a semi-submersible platform. The pipes, having a first end extending toward the semi-submersible platform and a second end extending toward the seabed. The pipe may be configured to facilitate the transport of liquid material from the seabed toward the surface of the sea and/or the semi-submersible platform. The pipes may be disposed in the ocean in a coplanar curtain. The method may further comprise controlling the angle of inclination of the pipes at the first end of the pipes. Controlling the angle of inclination may be accomplished using a bearing disposed on the semi-submersible. The bearing may be a gimbal.

A method of storing oil is provided. The method may comprise providing a semi-submersible vehicle having an upper portion and a lower portion. The lower portion may comprise a rectangular ring (as used herein rectangular ring may also include a square ring). The method may comprise facilitating the introduction of water into the rectangular ring. The method may comprise facilitating the introduction of liquid material, such as oil, into the rectangular ring. The liquid material may displace the water. The method may comprise treating the displaced water to remove contaminants.

In FIG. 6, the jacket is shown moored to the floating dock. FIG. 6 illustrates the jacket with the floating dock, after the foundations have been cut through. In this configuration, examinations of the state and/or configuration of the jacket may be performed to determine the condition of the jacket. For example, corrosion of the jacket may be determined. Corrosion may substantially alter the structural rigidity of the jacket and may be a significant issue during the rotation and/or de-ballasting of the jacket. Other issues may also be investigated, such as the quality of the welds, the completeness of the structure, the quality and/or availability of drain holes, the location of the jacket, the profile of the seabed floor, and/or other issues related to the decommissioning of the jacket. The jacket may be more safely rotated while submerged (e.g. either entirely or partially) since the stresses may be reduced. The jacket sections may or may not be complete structurally. The extent of flooding of the jacket columns and cross bracing may be determined. In some implementations, provisions may be made for the introduction of compressed air into the jacket (e.g. at the top of each column). Jacket drain holes may be remotely operated such that the valves may be fitted at one or more column bottoms.

In some implementations, strand jacks may be connected to the jacket and provide vertical lifting and/or rotation access on the jacket. Vertical lifting and/or rotation of the jacket may be assisted by the de-ballasting sequence of the jacket. The jacket may have compartments including one or more vent line(s). The vent line(s) may be used to introduce air and/or to eject seawater from the jacket. The introduction of air and/or ejection of seawater from the jacket may create buoyancy (e.g. a buoyant force) that rotates the jacket into a vertical plane and/or about an axes of the jacket. For example, seawater may be pumped out from the columns of the jacket such that a buoyant forte acts on the jacket. The buoyant force may act to lift the jacket generally, or the force may apply a turning moment on the jacket to rotate the jacket to the surface. The turning moment may tend to rotate the jacket in a horizontal configuration

Air compressors may be installed on the floating dock, the jacket, and/or in other configurations. Air compressors may introduce air at column tops of the jacket for de-ballasting. The air compressors may expel water from the holes at the bottom of the columns (e.g. drain holes). In some implementations, two hundred tonnes of air may be consumed to de-ballast a jacket column. For example, a 1000 hp air compressor may de-ballast a jacket column (200 tonnes of air) in approximately twelve hours.

In some implementations, stresses may be catastrophic during de-ballasting. In some implementations, the stresses may exceed the ultimate strength of the shell plating and internal bulkheads. Stress analysis may determine if the jacket columns are able to withstand structural stresses generated by the pressurized air (e.g. hoop stresses). In some implementations, the stresses may exceed 200 psi. Jacket structures may be analyzed for the pressurized air from the air compressors to determine if acceptable factors of safety and/or margins of safety exist for the determined stresses that may be induced on the structure.

Compressed air may be introduced at jacket column tops. De-ballasting may commence in a sequence that tends to lift and/or rotate the jacket towards the horizontal. The de-ballasting may be guided and/or assisted by pulling with attached strands to lift and/or rotate the jacket. Periodically, the de-ballasting may be stopped to check for air leaks. De-ballasting may be stopped to determine the integrity of the structure, rigging, and/or jacket. The de-ballasting forces may tend to lift and/or rotate the jacket. In some forces the de-ballasting forces rotating or lifting the jacket may be stopped to verify the angle and/or position of the jacket relative to the floating dock opening(s) and/or for other reasons. In some implementations, the de-ballasting may be reversed and the jacket columns ballasted in order to correctly align or assist the lift and/or rotation of the jacket The de-ballasting and/or lifting-process may be reversed to set the jacket down on the seabed floor.

De-ballasting may continue until the jacket is buoyant. For example, the de-ballasting may result in the jacket floating on a water-surface horizontally. De-ballasting may result in the floatation of the jacket due to the jackets buoyancy. The de-ballasted buoyant jacket may then be enclosed within the floating dock and securely towed from the site. The floating dock bottom may be closed by buoyant floating gate(s) to enclose or surround the buoyant jacket. The jacket may be set down on gates of the floating dock. In some implementations, the jacket may be elevated onto a barge and drained. The floating dock may be deballasted to elevate and drain the jacket. For example, the floating dock may be completely de-ballasted (e.g. drained of seawater) so that the resistance to towing is minimized. The floating dock may then be towed to shore (e.g. by tugs and/or barges). The end gate of the floating dock and/or the buoyant floating gates may be removed providing access to the jacket. The floating dock may be aligned and/or elevated to remove the jacket. For example, the jacket and/or floating dock may be pulled out of the water. The jacket may be supported by the floating dock or raised onto a floating vessel.

FIG. 7 illustrates a semi-submersible marine vessel 700 configured for removing fixed offshore platforms such as steel piled jackets. The semi-submersible marine vessel 700 may comprise a main body 705, a mooring system 710, a lifting system having a plurality of strand jacks 715 and plurality of strand jack cables 720, and a gate 725 disposed at the second end. The main body 705 may have an extended shape sized to house a fixed offshore platform oriented in a prone position. The main body 705 may have a first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position. In some implementations, the main body 705 may comprise steel plates. The main body 705 may include a lower portion 730 and an upper portion 735, the lower portion 730 being configured to provide sufficient buoyancy to maintain the upper portion 735 above a waterline, and wherein the lower portion 730 is configured to store air or liquid matter. In one example the liquid matter stored in the lower portion 730 comprises one or more of sea water, and/or ballast water. The main body 705 may include a plurality of vertically disposed columns 740 extending between the upper 735 and the lower 730 portions of the vessel and a plurality of horizontally disposed pontoons 745 extending between adjacent columns 740 proximal to the lower portion 730.

In FIG. 8(A) and FIG. 8(B), the lower portion is shown to comprise two or more compartments such that at least some adjacent compartments are in fluid contact with each other. As an example, the lower portion may be comprised of tubular elements. The tubular elements may resemble rectangular blocks. The lower portion may comprise a plurality of cubic boxes. Individual tubular elements and/or cubic boxes may be operably connected to adjacent r tubular elements and in fluid contact with one another. The tubular elements and/or cubic boxes may be connected through one or more of welding, riveting, sticking, mechanical seal, construing, and/or other connecting methods. The tubular elements and/or cubic boxes may be formed of metal. The tubular elements and/or cubic boxes may be formed from an alloy. The tubular elements and/or cubic boxes may be formed of steel. As used herein, the term tubular elements is intended to encompass tubular elements having walls with equal dimensions, forming a square, as well as tubular elements having walls with different dimensions.

In some implementations, the lower portion 730 may include a plurality of swivel fairleaders 750, configured to enhance the stability of the vessel and prevent the semi-submersible marine vessel 700 from rolling over. In some implementations, the upper portion 735 may comprise a plurality of mooring winches 755.

The mooring system 710, configured to moor the vessel 700 to the seabed and facilitate maneuvering onto and around fixed offshore platform jackets, may include a first end operatively connected to the semisubmersible vessel configured to secure the mooring system to the vessel, a second end configured to secure the mooring system to the seabed, and a line between the first end and the second end configured to facilitate the mooring of the vessel to the seabed, wherein the line between the first end and the second end is arranged in catenary. The line may be a neutrally buoyant line. In some implementations, the second end of the mooring system further comprises an anchor configured to anchor the mooring system to the seabed. The second end of the mooring system may include a deadweight. In some implementations, the first line portion may comprise a chain. In some implementations, the first line portion may include a cable.

The lifting system may further comprise a plurality of gantry cranes 760 mounted on rails on the upper portion.

The gate 725 may be a neutrally buoyant gate. The gate 725 may be opened via removal and flotation on water. In some implementations, the gate 725 may be affixed to the main body 705 via hinges configured to facilitate opening and dosing of the gate.

In some implementations, the semi-submersible marine vessel 700 may include a plurality of azimuth thrusters. The azimuth thrusters may enable self-propulsion of the vessel and eliminate the need for tugs. The azimuth thrusters may be disposed at one or more corner of the lower portion of the main body 705 and/or other locations on the main body 705. In some implementations, the azimuth thrusters may be retractable. This may reduce the depth of water needed to enter a dock.

FIGS. 9(A)-9(D) and FIG. 10 illustrate a method 1000 for decommissioning fixed offshore platforms such as steel piled jackets. The operations of method 1000 presented below are intended to be illustrative. In some implementations, method 1000 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method 1000 are illustrated in FIG. 10 and described below is not intended to be limiting.

Operation 1005 may comprise maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket. The semi-submersible marine vessel may include a main body (e.g., main body 705) having an extended shape sized to house a fixed offshore platform oriented in a prone position. The main body may have a first end opposing a second end and a first side opposing a second side. The first end and the second end may have dimensions that exceed dimensions of a footprint of the fixed offshore platform. The first side and the second side may have dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position. The semi-submersible may include a lifting system having a plurality of strand jacks (e.g., strand jacks 715) and a plurality of strand jack cables (e.g., strand cables 720). The semi-submersible may include a mooring system (e.g., mooring system 710). The semi-submersible may include a gate (e.g., gate 725) disposed at the second end.

Operation 1010 may include opening the gate.

Operation 1015 may include surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body.

Operation 1020 may include ballasting the main body so that a lower portion (e.g., lower portion 730) of the main body is submerged in the water.

Operation 1025 may include attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket.

Operation 1030 may include affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting or rotating the fixed offshore platform jacket.

Operation 1035 may include deballasting the main body in order to free the offshore platform jacket from seabed.

Operation 1040 may include rotating the fixed offshore platform jacket under water from a vertical position to a prone position.

Operation 1045 may include housing the fixed offshore platform jacket oriented in the prone position within the main body to enable transport of the semi-submersible marine vessel towards a dry-dock.

Operation 1050 may include dosing the gate.

Operation 1055 may include guiding the semi-submersible marine vessel towards the dry-dock. Affecting the buoyancy of the fixed offshore platform jacket 1030 may include filling at least a portion of the fixed offshore platform jacket with compressed air. The affected buoyancy of the fixed offshore platform jacket may be at or near neutrally buoyant in sea water.

The jacket is rotated and lifted while underwater to reduce stress on the structure then pulled in the semi-submersible marine vessel.

In some implementations, the removal of the jacket from seabed is achieved through processes known in the art such as explosion charge cutoff or using cables studded with industrial diamonds to cut the bases off. It is noted that due to deterioration of the jacket and the welded areas around the jacket, the metal is refurbished as much as possible prior to at least partially filling the jacket.

In regards to the guiding the vessel to a dry dock, as the vessel nears a shore, the process is started by reducing draft and raising the vessel. As an example, a 20 meter pontoon is raised about 7 to 8 meters so that it can enter a channel. Since channels are generally about 9 meters, it is desired that the vessel follow a straight path into the dry dock, proceeding by dosing the gate and setting the jacket down. As the vessel is raised up, it has a tendency to roll over in the water plane area, due to conflict in the vertical center of gravity. To compensate for this anomaly, the vessel is raised at an angle. As an example vessel is raised at 1° angle. As the lower portion of the vessel approaches the waterline, the pontoons are used to stabilize the vessel and dampen the motions caused by the draft.

FIG. 11 illustrates a semi-submersible marine vessel 1100 configured for removing fixed offshore platforms such as steel piled jackets. The semi-submersible marine vessel may include a main body 1105 sized to surround a portion of a fixed offshore platform oriented in a vertical position, a mooring system 1110, and a lifting system having a plurality of strand jacks 1115 and a plurality of strand jack cables 1120. The main body 1105 may have a first end and a first side opposing a second side, the first end having dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position, the first side and the second side having dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension In some implementations, the main body 1105 may include steel plates. The main body 1105 may include a lower portion 1125 and an upper portion 1130, the lower portion 1125 being configured to provide sufficient buoyancy to maintain the upper portion 1130 above a waterline, and wherein the lower portion 1125 is configured to store air or liquid matter. In one example the liquid matter stored in the lower portion 1125 comprises one or more of sea water, and/or ballast water. The main body 1105 may further include a plurality of vertically disposed columns 1135 extending between the upper 1130 and the lower 1125 portions of the vessel and a plurality of horizontally disposed pontoons 1140 extending between adjacent columns 1135 proximal to the lower portion 1125.

In FIGS. 12(A) and 12(B), the lower portion is shown to include two or more compartments such that at least some adjacent compartments are in fluid contact with each other. As an example, the lower portion may be comprised of tubular elements. The tubular elements may resemble rectangular blocks. The lower portion may include a plurality of cubic boxes. Individual tubular elements and/or cubic boxes may be operably connected to adjacent r tubular elements and in fluid contact with one another. The tubular elements and/or cubic boxes may be connected through one or more of welding, riveting, sticking, mechanical seal, construing, and/or other connecting methods. The tubular elements and/or cubic boxes may be formed of metal. The tubular elements and/or cubic boxes may be formed from an alloy. The tubular elements and/or cubic boxes may be formed of steel. As used herein, the term tubular elements is intended to encompass tubular elements having walls with equal dimensions, forming a square, as well as tubular elements having walls with different dimensions.

In some implementations, the lower portion 1125 may include a plurality of swivel fairleaders 1145, configured to enhance the stability of the vessel and prevent the vessel from rolling over. In some implementations, the upper portion 1130 may include a plurality of mooring winches 1150.

The mooring system 1110, configured to moor the vessel to the seabed and facilitate maneuvering onto and around fixed offshore platform jackets, may include a first end operatively connected to the semisubmersible vessel configured to secure the mooring system to the vessel, a second end configured to secure the mooring system to the seabed, and a line between the first end and the second end configured to facilitate the mooring of the vessel to the seabed, wherein the line between the first end and the second end is arranged in catenary. The line may be a neutrally buoyant line. In some implementations, the second end of the mooring system may include an anchor configured to anchor the mooring system to the seabed. The second end of the mooring system may comprise a deadweight. In some implementations, the first line portion may indude a chain. In some implementations, the first line portion may include a cable.

The lifting system may further include a plurality of gantry cranes 1155 mounted on rails on the upper portion 1130.

The semi-submersible marine vessel 1100 may further indude a gate (not shown) disposed at the second end. In some implementation, the gate may be a neutrally buoyant gate. The gate may be opened via removal and flotation on water. In some implementations, the gate may be affixed to the main body via hinges configured to facilitate opening and closing of the gate.

In some implementations, the semi-submersible marine vessel 1100 may include a plurality of azimuth thrusters. The azimuth thrusters may enable self-propulsion of the vessel and eliminate the need for tugs. The azimuth thrusters may be disposed at one or more corner of the lower portion of the main body 1105 and/or other locations on the main body 1105. In some implementations, the azimuth thrusters may be retractable. This may reduce the depth of water needed to enter a dock.

FIGS. 13 and 14 illustrate a method for decommissioning fixed offshore platforms such as steel piled jackets. The operations of method 1400 presented below are intended to be illustrative. In some implementations, method 1400 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method 1400 are illustrated in FIG. 14 and described below is not intended to be limiting.

Operation 1405 may include maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket. The semi-submersible marine vessel may include a main body (e.g., main body 1105) sized to surround a portion of a fixed offshore platform oriented in a vertical position. The semi-submersible marine vessel may include a lifting system having a plurality of strand jacks (e.g., strand jacks 1115) and a plurality of strand jack cables (e.g., strand jack cables 1120). The semi-submersible marine vessel may include a mooring system (e.g., mooring system 1110) and a gate. The main body may have a first end and a first side opposing a second side. The first end may have dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position. The first side and the second side may have dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension.

Operation 1410 may include opening the gate.

Operation 1415 may include surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body.

Operation 1420 may include ballasting the main body so that a lower portion (e.g. 1125) of the main body is submerged in the water.

Operation 1425 may include attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket.

Operation 1430 may include affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting.

Operation 1435 may include deballasting the main body in order to free the offshore platform jacket from a seabed.

Operation 1440 may include housing the fixed offshore platform jacket oriented in the vertical position within the main body to enable transport of the fixed offshore platform jacket above the seabed surface.

Operation 1445 may include closing the gate.

Operation 1450 may include guiding the semi-submersible marine vessel towards a higher elevation along an inclined surface of seabed.

Operation 1455 may include setting the fixed offshore platform jacket down vertically on the inclined surface of seabed.

Operation 1460 may include cutting an exposed top portion of the fixed offshore platform jacket.

Operation 1465 may include loading the cut potion on a barge in order to be shipped to shore for further processing.

Operations 1420-1465 may be repeated as necessary in order to completely remove the fixed offshore platform jacket from water. Affecting the buoyancy 1430 of the fixed offshore platform jacket may include filling at least a portion of the fixed offshore platform jacket with compressed air. The affected buoyancy of the fixed offshore platform jacket may be at or near neutrally buoyant in sea water. It is noted that the fixed offshore platform jacket remains in the vertical orientation throughout the decommissioning process. In some implementations, the topside may remain attached to the fixed offshore platform jacket when the fixed offshore platform jacket is being lifted off seabed. In some implementations, the topside may be removed prior to the fixed offshore platform jacket being lifted off seabed. In some implementations, the removal of the jacket from seabed is achieved through processes known in the art such as explosion charge cutoff or using cables studded with industrial diamonds to cut the bases off.

Although the system(s) and/or method(s) of this disclosure have been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred implementations, it is to be understood that such detail is solely for that purpose and that the disclosure is not limited to the disclosed implementations, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any implementation can be combined with one or more features of any other implementation. 

What is claimed is:
 1. A semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets, the semi-submersible marine vessel comprising: a main body having an extended shape sized to house a fixed offshore platform oriented in a prone position, the main body having first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position; a mooring system; a lifting system having a plurality of strand jacks and a plurality of strand jack cables; and a gate disposed at the second end.
 2. The semi-submersible marine vessel of claim 1, wherein the main body has a lower portion and an upper portion, the lower portion being configured to provide sufficient buoyancy to maintain the upper portion above a waterline, and wherein the lower portion is configured to store air or liquid matter.
 3. The semi-submersible marine vessel of claim 1, wherein the main body comprises steel plates.
 4. The semi-submersible marine vessel of claim 1, further comprising a plurality of vertically disposed columns extending between the upper and the lower portions of the vessel.
 5. The semi-submersible marine vessel of claim 1, further comprising a plurality of horizontally disposed pontoons extending between adjacent columns proximal to the lower portion.
 6. The semi-submersible marine vessel of claim 1, wherein the upper portion comprises a plurality of mooring winches.
 7. The semi-submersible marine vessel of claim 1, wherein the lower portion comprises two or more compartments such that at least some adjacent compartments are in fluid contact with each other.
 8. The semi-submersible marine vessel of claim 1, wherein the lower portion comprises a plurality of swivel fairleaders.
 9. The semi-submersible marine vessel of claim 1, wherein the gate is a neutrally buoyant gate.
 10. The semi-submersible marine vessel of claim 1, wherein the mooring system comprises: a first end operatively connected to the semisubmersible vessel configured to secure the mooring system to the vessel; a second end configured to secure the mooring system to the seabed; and a line between the first end and the second end configured to facilitate the mooring of the vessel to the seabed, wherein the line between the first end and the second end is arranged in catenary.
 11. The semi-submersible marine vessel of claim 1, wherein the lifting system further comprises: a plurality of gantry cranes mounted on rails on the upper portion.
 12. The semi-submersible marine vessel of claim 2, wherein the liquid matter stored in the lower portion comprises one or more of sea water, and/or ballast water.
 13. The semi-submersible marine vessel of claim 9, wherein the gate is opened via removal and flotation on water.
 14. The semi-submersible marine vessel of claim 9, wherein the gate is affixed to the vessel via hinges configured to facilitate opening and closing of the gate.
 15. The semi-submersible marine vessel of claim 10, wherein the line is a neutrally buoyant line.
 16. The semi-submersible marine vessel of claim 10, wherein the second end of the mooring system further comprises an anchor configured to anchor the mooring system to the seabed.
 17. The semi-submersible marine vessel of claim 10, wherein the second end of the mooring system further comprises a deadweight.
 18. The semi-submersible marine vessel of claim 10, wherein the line is a neutrally buoyant line.
 19. The semi-submersible marine vessel of claim 10, wherein the first line portion is a chain.
 20. The semi-submersible marine vessel of claim 10, wherein the first line portion is a cable.
 21. A method for decommissioning fixed offshore platforms such as steel piled jackets, the method comprising: maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket, the semi-submersible marine vessel comprising: a main body having an extended shape sized to house a fixed offshore platform oriented in a prone position, the main body having first end opposing a second end and a first side opposing a second side, the first end and the second end having dimensions that exceed dimensions of a footprint of the fixed offshore platform, the first side and the second side having dimensions that exceed dimensions of the fixed offshore platform oriented in a prone position; a mooring system; a lifting system having a plurality of strand jacks and a plurality of strand jack cables; and a gate disposed at the second end; opening the gate surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body; ballasting the main body so that the a lower portion of the main body is submerged in the water; attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting or rotating the fixed offshore platform jacket; deballasting the main body in order to free the offshore platform jacket from seabed; rotating the fixed offshore platform jacket under water from a vertical position to a prone position; housing the fixed offshore platform jacket oriented in the prone position within the main body to enable transport of the semi-submersible marine vessel towards a dry-dock; closing the gate; and guiding the semi-submersible marine vessel towards the dry-dock.
 22. The method of claim 21, wherein affecting the buoyancy of the fixed offshore platform jacket includes filling at least a portion of the fixed offshore platform jacket with compressed air.
 23. The method of claim 21, wherein the affected buoyancy of the fixed offshore platform jacket is at or near neutrally buoyant in sea water.
 24. A semi-submersible marine vessel configured for removing fixed offshore platforms such as steel piled jackets, the semi-submersible marine vessel comprising: a main body sized to surround a portion of a fixed offshore platform oriented in a vertical position, the main body having a first end and a first side opposing a second side, the first end having dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position, the first side and the second side having dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension; a mooring system; and a lifting system having a plurality of strand jacks and a plurality of strand jack cables.
 25. The semi-submersible marine vessel of claim 1, wherein the main body has a lower portion and an upper portion, the lower portion being configured to provide sufficient buoyancy to maintain the upper portion above a waterline, and wherein the lower portion is configured to store air or liquid matter.
 26. The semi-submersible marine vessel of claim 1, wherein the main body comprises steel plates.
 27. The semi-submersible marine vessel of claim 1, further comprising a plurality of vertically disposed columns extending between the upper and the lower portions of the vessel.
 28. The semi-submersible marine vessel of claim 1, further comprising a plurality of horizontally disposed pontoons extending between adjacent columns proximal to the lower portion.
 29. The semi-submersible marine vessel of claim 1, wherein the lower portion comprises two or more compartments such that at least some adjacent compartments are in fluid contact with each other.
 30. The semi-submersible marine vessel of claim 1, further comprising a gate disposed opposite to the first end.
 31. The semi-submersible marine vessel of claim 1, wherein the upper portion comprises a plurality of mooring winches.
 32. The semi-submersible marine vessel of claim 1, wherein the lower portion comprises a plurality of swivel fairleaders.
 33. The semi-submersible marine vessel of claim 1, wherein the mooring system comprises: a first end operatively connected to the semisubmersible vessel configured to secure the mooring system to the vessel; a second end configured to secure the mooring system to the seabed; and a line between the first end and the second end configured to facilitate the mooring of the vessel to the seabed, wherein the line between the first end and the second end is arranged in catenary.
 34. The semi-submersible marine vessel of claim 1, wherein the lifting system further comprises: a plurality of gantry cranes mounted on rails on the upper portion.
 35. The semi-submersible marine vessel of claim 2, wherein the liquid matter stored in the lower portion comprises one or more of sea water, and/or ballast water.
 36. The semi-submersible marine vessel of claim 7, wherein the gate is a neutrally buoyant gate.
 37. The semi-submersible marine vessel of claim 10, wherein the line is a neutrally buoyant line.
 38. The semi-submersible marine vessel of claim 10, wherein the second end of the mooring system further comprises an anchor configured to anchor the mooring system to the seabed.
 39. The semi-submersible marine vessel of claim 10, wherein the second end of the mooring system further comprises a deadweight.
 40. The semi-submersible marine vessel of claim 10, wherein the line is a neutrally buoyant line.
 41. The semi-submersible marine vessel of claim 10, wherein the first line portion is a chain.
 42. The semi-submersible marine vessel of claim 10, wherein the first line portion is a cable.
 43. The semi-submersible marine vessel of claim 13, wherein the gate is opened via removal and flotation on water.
 44. The semi-submersible marine vessel of claim 13, wherein the gate is affixed to the vessel via hinges configured to facilitate opening and closing of the gate.
 45. A method for decommissioning fixed offshore platforms such as steel piled jackets, the method comprising: maneuvering a semi-submersible marine vessel towards a fixed offshore platform jacket, the semi-submersible marine vessel comprising: a main body sized to surround a portion of a fixed offshore platform oriented in a vertical position, the main body having a first end and a first side opposing a second side, the first end having dimensions that exceed a first lateral dimension of the fixed offshore platform oriented in a vertical position, the first side and the second side having dimensions that exceed a second lateral dimension of the fixed offshore platform oriented in a vertical position, the first lateral dimension being perpendicular to the second lateral dimension; a lifting system having a plurality of strand jacks and a plurality of strand jack cables; a mooring system; and a gate; opening the gate surrounding the fixed offshore platform jacket with the semi-submersible marine vessel main body; ballasting the main body so that a lower portion of the main body is submerged in the water; attaching the fixed offshore platform jacket to the strand jack cables at two or more points on the fixed offshore platform jacket affecting a buoyancy of the fixed offshore platform jacket to facilitate lifting; deballasting the main body in order to free the offshore platform jacket from a seabed; housing the fixed offshore platform jacket oriented in the vertical position within the main body to enable transport of the fixed offshore platform jacket above the seabed surface; closing the gate; guiding the semi-submersible marine vessel towards a higher elevation along an inclined surface of seabed; setting the fixed offshore platform jacket down vertically on the inclined surface of seabed; cutting an exposed top portion of the fixed offshore platform jacket; loading the cut potion on a barge in order to be shipped to shore for further processing; and repeating the previous steps as necessary to completely remove the fixed offshore platform jacket from water.
 46. The method of claim 22, wherein affecting the buoyancy of the fixed offshore platform jacket includes filling at least a portion of the fixed offshore platform jacket with compressed air.
 47. The method of claim 22, wherein the affected buoyancy of the fixed offshore platform jacket is at or near neutrally buoyant in sea water. 